1. Field of the Invention
The present invention relates to a fluorescent glass dosimeter utilized for measuring a radiation exposure dose of a radiation equipment operator, a spatial dose distribution inside and around radiation equipment such as a power-generating atomic reactor, an exposure dose upon radiotherapeutics and, more particularly, to a fluorescent glass dosemeter having improved glass element holder and holder case.
2. Description of the Related Art
In general, the more the amount of energy, i.e., radiation dose, a living body is exposed the more the body is in danger and the more the environment is negatively influenced. Therefore, persons who install an atomic reactor, an accelerator, an X-ray generator, and a radioisotope must perfectly manage radiation, and for operators and users, measurement of radiation dose is inevitable. For this reason, the role of a dosimeter for measuring a radiation dose with high precision is increasingly important.
In a fluorescent glass dosimeter, a glass element holder for holding a fluorescent glass element and a holder case for storing the holder constitute a capsule. During operation, the capsule storing the glass element holder is carried or is equipped on a proper location, and upon measurement, a large number of capsules are automatically loaded to a dose read-out instrument using a magazine or are manually set therein to measure a radiation dose.
In the conventional fluorescent glass dosimeter described above, in particular, in the glass element holder, as shown in FIG. 7, fluorescent glass element 1 is fitted in outer holder 2 from a direction indicated by an arrow (A) in FIG. 7 while being in sliding contact therewith. Fluorescence detection window 3 having a size slightly smaller than the outer shape of fluorescent glass element 1 is formed in outer holder 2, and " "-shaped bent segments 4 for holding glass element 1 are provided on two side edge portions of outer holder 2 on a side perpendicular to a glass element insertion direction. Anti-removal pawls 5 are provided on portions of bent segments 4, i.e., end portions on the glass element insertion side and positions separated from the end portions by a predetermined distance.
Therefore, in such a glass element holder, fluorescent glass element 1 is inserted to a predetermined position of outer holder 2 along the direction indicated by an arrow (A) in FIG. 7. Thereafter, pawls 5 are pressed and bent from the direction indicated by an arrow (B) in FIG. 7, thereby fixing fluorescent glass element 1 in outer holder 2. When a radiation dose is measured, a capsule is placed on measurement table 6, as shown in FIG. 8. When ultraviolet rays 7 are incident on fluorescent glass element 1 from a narrow side surface thereof from the direction indicated by an arrow in FIG. 8, fluorescence 8 based on a radio photoluminescence phenomenon is detected from a wide surface of fluorescent glass element 1 in a direction perpendicular to the ultraviolet ray incident direction, and a radiation dose is measured from the intensity of fluorescence 8.
A case for storing the glass element holder is divided into upper and lower cases 11 and 12, as shown in FIGS. 9 and 10. Slide grooves 13a and 13b are formed at positions relatively adjacent to side walls of upper case 11 in a direction of thickness. L-shaped lock projection member 15 is suspended at an intermediate portion between slide grooves 13a and 13b. Reference numerals 16a and 16b denote recesses formed in the groove surfaces. Slide segments 18a and 18b having, on their outer side surfaces, projections 17a and 17b respectively engaged with recesses 16a and 16b, are provided to lower case 12. Metal member 19, which is normally biased to the right indicated by an arrow in FIG. 10 by a leaf spring (now shown), is arranged inside lower case 12. Inverted L-shaped lock projection member 20 is mounted on the bottom surface of lower case 12. Four jig insertion square holes 21 are formed in the outer bottom surface of lower case 12 at predetermined intervals. Reference numeral 22 denotes a storage portion for glass element holder.
Therefore, in this capsule, after the glass element holder shown in FIG. 7 is stored in storage portion 22 of lower case 12, slide segments 18a and 18b of lower case 12 are inserted in slide grooves 13a and 13b. Before insertion, metal member 19 of lower case 12 is urged against the inner side surface of inverted L-shaped lock projection 20. When lower case 12 is inserted in upper case 11, L-shaped projection 15 of upper case 11 urges metal member 19 to the left in FIG. 10 to move it to the position shown in FIG. 10. When lower case 12 is completely inserted, metal member 19 is returned to an original position by the leaf spring and is clamped between projections 15 and 20 to make a lock. And projections 17a and 17b of lower case 12 are engaged with recesses 16a and 16b of the upper case to make an auxiliary lock.
When the lock is to be released, a magnet approaches from outside slide segment 18a, metal member 19 is attracted on the inner wall of slide segment 18a to be unlocked. Thus, lower case 12 can be removed from upper case 11.
However, the above-mentioned capsule poses the following problems. First, in the glass element holder, both side edge portions of fluorescent glass element 1 in a direction perpendicular to the glass element insertion direction are masked with bent segments 4 of outer holder 2. However, other edges, in particular, edge portions (C) on the side of the detection surface are not masked. Therefore, detection sensitivity varies depending on a chamfering width of the edge portion (C), and this variation causes the large influence on measurement precision. Fluorescent glass element 1 is fixed by bending pawls 5 of outer holder 2. However, the bending operation is cumbersome, and may damage fluorescent glass element 1.
In the holder case, cases 11 and 12 are manually engaged. Upon removal of the cases, a jig is inserted in four square holes 21 of lower case 12 to clamp it, and then, upper case 11 is removed. However, the slide length corresponds to the direction of thickness and hence is short. For this reason, upon removal, it is difficult to apply a relatively large and uniform force to cases 11 and 12. In addition, if upper case 12 is removed while being slightly inclined, slide segments 18a and 18b may be damaged. In a fluorescent glass dosimetry system, a large number of capsules are sequentially loaded to a dose read-out instrument, while the glass element holder is removed from each case to read a radiation dose. When a predetermined dose is measured, the glass element holder is removed from cases 11 and 12. Since the case is opened/closed in the vertical direction, it is difficult to automate the opening/closing mechanism. For this reason, the case cannot be quickly and reliably opened/closed Cases 11 and 12 are locked by inserting metal member 19 between L-shaped lock projections 15 and 20. However, the lock function is not effective since the slide length corresponds to the direction of thickness of the capsule and hence is short. Recesses 16a and 16b and projections 17a and 17b are provided to the slide portions to effect an auxiliary lock. However, the lock mechanism is complicated accordingly, and reliability is inevitably degraded. Upon removal of the case, the jig is inserted in square holes 21 of lower case 12. The outer shape of the capsule is small, e.g., 2.times.3 cm, and the opening of each square hole 21 is very small. For this reason, it is difficult to insert the jig therein. Since cases 11 and 12 are plastic injection-molded products, projections for engaging the jig with square holes 21 cannot be formed. For this reason, upon removal of the case, lower case 12 is often removed from the jig, thus disturbing a removal operation.